1. Field of the Invention
This invention relates to an entertainment system comprised of plural entertainment devices interconnected via a communication channel, such as a telephone network, a picture display apparatus for outputting picture signals to a display unit in synchronism with external synchronization signals, an information processing apparatus for interconnecting plural information equipments having the above picture display apparatus via a communication network for transmitting data, and a synchronization controlling method for synchronizing plural picture signals and outputting the synchronized picture signals to the display unit.
2. Description of Related Art
It is currently practiced to interconnect information equipments, such as computer game playing machines, adapted for generating picture signals based on an application program for displaying the generated signal on a display apparatus, over communication networks, such as radio or wired communication networks, in order to process the information in real-time under exchanging data.
FIG. 1 shows the structure of a conventional game playing machine in which two game playing machines are interconnected over a communication cable in order to have a 1:1 combat game. This structure is used when the two game playing machines are in extremely close proximity to each other, as in home.
A game playing machine 81a (game playing machine A) and a game playing machine 81b (game playing machine B), interconnected over a communication cable (serial cable) 82, are provided with CRT controllers (CRTCs) 34a, 34b operating as display control means. These game playing machines 81a, 81b generate pictures based on the operating information of a controller connected to an own machine or on game process change data (status change information) indicating changes in the game progressing state. The game playing machines 81a, 81b also generate a picture based on operational data sent from other than the own machine. These pictures are collected by the CRTCs 34a, 34b to respective sole picture signals (video-out-A, video-out-B) which are outputted to respective display units 10a, 10b of the game playing machines 81a, 81b. 
FIG. 2 shows the structure of a conventional game playing apparatus in which three or more game playing machines are interconnected via a communication cable to carry out a game by a large number of participants. Similarly to the structure of FIG. 1, this structure is used in case the game playing machines are in close proximity to one another.
In FIG. 2, only three game playing machines 81a, 81b, 81c (game playing machines A, B and C) are shown. However, this number is merely illustrative and can be increased or decreased in desired manner. The communication cables (serial cables) 82a, 82b, 82c, . . . connected to the game playing machines are interconnected to a multi-tap 88 for relaying data transferred between the game playing machines.
The game playing machines interconnected by the communication cables 82a to 82c generate a picture based on operating data of the controller connected to the own machine, while also generating pictures based on game process change data (status change information) supplied form other than the own machine. These pictures are outputted as sole output picture signal (video-out-A, video-out-B and video-out-C) to display devices 10a, 10b, 10c. 
The structure in which plural game playing machines are remote from one another and in which a game is played as data such as game process change data are exchanged via communication network such as a telephone network.
FIG. 3 shows a structure of a conventional game playing apparatus in which two game playing machines, that is a game playing machine 81a (game playing machine A) and a game playing machine 81b (game playing machine B) are interconnected by a telephone network 82 in order to play a 1:1 combat game. This structure, similar to the structure of the game playing apparatus shown in FIG. 1, differs therefrom in that communication modems 83a, 83b are arranged for exchanging data over a telephone network 82. The parts or components similar to those described above are depicted by the same reference numerals.
FIG. 4 shows a structure in which three or more game playing machines are interconnected via telephone network 82a, 82b, 82c, . . . to have a play for many participants. Although this structure is similar to that of the game playing machine shown in FIG. 2, the telephone network 82a, 82b, 82c connected to the respective game playing machines are connected to a host station 89 operating for relaying the data transferred between the respective game playing machines.
In the above-described structure, there is produced delay (latency) in transmission time since data such as game process change data transmitted via telephone network 82 are sent via communication modems 83a, 83b, 83c. Thus, it has not been possible to synchronize picture signals (video-out-A, video-out-B, video-out-C) displayed on the display units 10a, 10b, 10c of the game playing machines.
For example, if two players A, B execute an “auto racing game”, a car B operated by a player B is displayed on the screen of the game playing machine of the player A in addition to a car B operated by the player B. Similarly, the car A operated by the player A is displayed on the screen of the game playing machine of the player B in addition to a car B operated by the player B.
Since data such as game process change data for displaying the car B as the counterpart of combat on a screen of the game playing machine of the player A are transmitted via communication modem via telephone network, these data are delayed with respect to data such as game process change data for displaying the car A on the screen of the game playing machine of the player A. This applies for the side of the player B.
Therefore, if the player operates the car A as he or she views the car B of the counterpart of combat displayed on the game playing machine of the player A, correct game results cannot be obtained.
The above-described problem arises since the CRTC as display control means for controlling picture signals displayed on a display device usually does not have the external synchronization function of retrieving external synchronization signals to effect synchronization control, such that synchronization control cannot be realized even if synchronization signals are entered along with data such as game process change data.
These information equipments operate on the basis of respective time information (clocks). For information processing in real-time as data are exchanged over communication networks between respective information equipments, reset signals are first exchanged to reset the clocks. However, since the clock speeds differ from equipment to equipment, if slightly, and are changed with time, the speeds of execution of the respective information equipments drift gradually such that there arises a problem that picture signals generated by an information equipment and displayed on the display unit are not in agreement with those generated by data such as game process change data sent from another information equipment and displayed on the display unit.
Of course, if the updating interval of pictures displayed on the dis-play apparatus is shortened, the above drift can be reduced. However, if desired to generate picture signals in real-time using data such as game process change data from outside and to display the generated data, it is necessary to transfer data of large capacity such as game process change data in the face of considerable difficulties.
Thus, with the conventional picture display apparatus and the information processing apparatus employing these display apparatus, it has not been possible to execute information processing in need of high temporal accuracy by employing data such as game process change data transmitted via communication modem.